Allow empty return statements

src/macros.jl

@@ -1,9 +1,13 @@
 import MacroTools: splitdef, combinedef, isexpr, postwalk
 
-function find_return(stmt)
+# Check whether there are `return` statements that return something else but `nothing`
+function contains_return_something(stmt)
  result = false
  postwalk(stmt) do expr
- result |= @capture(expr, return x_)
+ if @capture(expr, return x_)
+ # `nothing` indicates a stand-alone return statement, `:nothing` indicates a `return nothing`
+ result |= x !== nothing && x !== :nothing
+ end
  expr
  end
  result
@@ -14,7 +18,9 @@ function __kernel(expr, generate_cpu=true, force_inbounds=false)
  def = splitdef(expr)
  name = def[:name]
  args = def[:args]
- find_return(expr) && error("Return statement not permitted in a kernel function $name")
+ if contains_return_something(expr)
+ error("Return statement (except `return` or `return nothing`) not permitted in kernel function $name")
+ end
 
  constargs = Array{Bool}(undef, length(args))
  for (i, arg) in enumerate(args)

test/test.jl

@@ -218,13 +218,64 @@ end
 
 @conditional_testset "return statement" skip_tests begin
  try
- @eval @kernel function kernel_return()
+ @eval @kernel function kernel_return1()
+ return 1
+ end
+ @test false
+ catch e
+ @test e.error ==
+ ErrorException("Return statement (except `return` or `return nothing`) not permitted in kernel function kernel_return1")
+ end
+ try
+ @eval @kernel function kernel_return2()
+ x = nothing
+ return x
+ end
+ @test false
+ catch e
+ @test e.error ==
+ ErrorException("Return statement (except `return` or `return nothing`) not permitted in kernel function kernel_return2")
+ end
+ try
+ @eval @kernel function kernel_return3()
+ return
+ end
+ @test true
+ catch e
+ @test false
+ end
+ try
+ @eval @kernel function kernel_return4()
+ return nothing
+ end
+ @test true
+ catch e
+ @test false
+ end
+ try
+ @eval @kernel function kernel_return5()
+ if something()
+ return something2()
+ end
+ something3()
  return
  end
  @test false
  catch e
  @test e.error ==
- ErrorException("Return statement not permitted in a kernel function kernel_return")
+ ErrorException("Return statement (except `return` or `return nothing`) not permitted in kernel function kernel_return5")
+ end
+ try
+ @eval @kernel function kernel_return6()
+ if something()
+ return
+ end
+ something3()
+ return
+ end
+ @test true
+ catch e
+ @test false
  end
 end